A number of fluid level sensing devices currently are available for determining the level of a fluid in a container. For example, in the oil and gas industry systems exist for measuring the levels of oil and water in a tank. One type of system, for example, utilizes ultrasonic technology. For this type of system, sound waves are directed from a remote location onto the surface of the fluid whose level is to be measured. These sound waves are reflected back and the time delay between the transmission of the initial waves and the sensed reflected waves indicates the fluid level of the fluid in the tank. Ultrasonic technology has proven inaccurate, however, as it is difficult to accurately predict the tank environment. Factors such as humidity, temperature fluctuations, pressure fluctuations, etc. make ultrasonic technology ill-suited for fluid level measurement.
A number of systems also have been developed using Reed switch technology. Generally, these devices include a rod assembly having a plurality of discrete Reed switches located along its length. A permanent magnet is provided, generally in the form of a float assembly, that floats on the surface of the fluid whose level is desired to be measured. As the float rises and falls with the fluid level, the magnetic field generated by the permanent magnet causes the Reed switches to close. The state of the Reed switches, being in either an open or closed configuration, indicates the fluid level. See, for example, U.S. Pat. Nos. 3,976,963; 4,730,491; 4,976,146; and 6,571,626. U.S. Pat. Nos. 4,589,282; 5,793,200 and 6,563,306 disclose similar systems but incorporate Hall effect sensors rather than Reed switches.
Published PCT application WO 97/13122 discloses a sensor system utilizing a rod assembly having a plurality of coils wound along its length. A float assembly having a combination resonator coil and capacitor or ferromagnetic coil interacts with the rod assembly coils to provide position location information from which the fluid level can be determined.
Systems such as those described above often include an integrally formed rod assembly that may be 20 to 30 feet in length. Transportation and installation of large numbers of rod assemblies having those lengths is difficult and expensive. The total cost of these systems also is affected by the implementation of Reed switches, which are a relatively expensive component. For Reed switch systems, the accuracy of the system is dependant on the number of switches spaced apart along the rod assembly. As such, the more accurate the system, the more costly it becomes.
In the oil and gas industry, a customer may have thousands of wells for which the fluid levels of multiple fluids are desired to be measured. For example, a typical tank will contain both oil and water, and a customer may desire to know the respective levels of both fluids. Water has a specific gravity of 1, while the specific gravity of crude oil, e.g., from California, Mexico, or Texas, ranges from between about 0.8 to about 0.9 at 60° F. The relative closeness of the specific gravities of oil and water makes simultaneous measurement of these fluid levels difficult.
Because of the number of wells and the relatively harsh conditions in which the wells are located, an advantageous fluid level indicator system must be easily shipped and installed, have a long lifespan, and require little maintenance. Such a system also must be readily able to accurately determine the fluid levels of multiple fluids contained with a tank. Generated well data must be easily accessible by the customer.